Method and apparatus for sensing flatness of metal sheet

ABSTRACT

A method of and apparatus for sensing and/or controlling the flatness or the shape of metal sheet or strip running under a predetermined tension comprising a plurality of sensors or suspended nozzles arranged transversely underneath the sheet or strip. The sheet or strip is supplied by the nozzles with a jetted gas of a controllable pressure p and suspended with an upwardly urging force not exceeding a value of 3Kg by means of a gas pressure q which is controllable independently from the jetted gas pressure p.

United States Patent [191 Ando et al. Nov. 26, 1974 [54] METHOD AND APPARATUS FOR SENSING 3,402,603 9/1968 Hollister et al. .1 73 159 FLATNESS 0 METAL SHEET 3,496,744 2/1970 Mizuno et al..... 72/12 3,499,306 3/1970 Pearson 72/17 [75] Inventors: Masao Ando; Yukiyasu Takeda,

both of Nagoya, Japan [73 Assignee: Sumitomo Light Metal Industries, Primary "M Mehr Ltd Tokyo, Japan Attorney, Agent, or FzrmBrowdy and Neimark [22] Filed: Nov. 19, 1973 [21] Appl. No.: 416,813 ABSTRACT [30] Foreign Application Priority Data A method of and apparatus for sensing and/or control- Nov. 17, 1972 Japan 47-116073 ling the flatness or the shape of metal sheet or strip Oct. 27, 1973 Japan 48-121137 running under a predetermined tension comprising a plurality of sensors or suspended nozzles arranged [52] US. Cl 73/37.7, 73/ 159, 72/10 transversely underneath the sheet or strip. The sheet [51] Int. Cl. G0lb 13/22, GOlb 13/16 or strip is supplied by the nozzles with a jetted gas of [58] Field of Search 72/8, 9, 10, 11, 12, 16, a controllable pressure p and suspended with an up- 72/17; 73/37], 159 wardly urging force not exceeding a value of 3Kg by Y means of a gas pressure q which is controllable inde- [56] References Cited pendently from the jetted gas pressure p.

UNITED STATES PATENTS I 2,985,399 5/1961 Digel..., 73/377 X 9 Claims, 11 Drawing Figures star METHOD AND APPARATUS FOR SENSING FLATNESS OF METAL SHEET FIELD OF THE INVENTION The present invention relates to an improved method of and an improved apparatus for non contacting sensing and/or controlling the shape or flatness of a metal sheet or strip running under tension. The sensing and- /or controlling is achieved by supplying compressed air to a plurality of separated nozzles arranged transversely to the direction of travel of the sheet or strip to form a jet and by applying axial loads to the nozzles which are movable longitudinally in a suspended state due to a balance between the jetting force and the axial load. Buckling or local deflection of the sheet is detected by analyzing the displacement variation between the nozzles.

BACKGROUND OF THE INVENTION The present invention relates to a method of and apparatus for sensing and/or controlling the flatness or the shape of a metal sheet or strip running under tension by a plurality of suspended nozzles arranged transversely underneath the sheet or strip. A prior art invention is known, i.e., Japanese Pat. No. 633,200 (U.S. Pat. No. 3,496,744), which teaches the fundamental principles and features of the instant invention which is an improvement over the prior art. The prior art patent teaches that the layer thickness 1 is proportional to gas pressure p of the reservoir and inversely proportional to the nozzle urging force W.

Furthermore, in the prior art nozzle units which are urged to the sheet by dead weight or by air pressure not independent from nozzle pressure it is difficult or impossible to remotely control the nozzle urging force W during operation. In such prior art devices air is com monly used for both nozzle exhausting pressure p and nozzle urging pressure q and frequently the pressure p is effected by the pressure q. But the drawback is completely removed in the present invention.

SUMMARY OF THE INVENTION The shortcomings of such prior art methods and apparatus are satisfactorily overcome by the present invention. Accordingly, an object of the present invention is to provide a method of and apparatus for sensing flatness of a running sheet under tension by a plurality of noncontacting suspending nozzles which are urged upwardly to the sheet by an urging force developed from the gas pressure (1 which is independently controllable from the nozzle jetting gas pressure p.

Another object of the present invention is to provide a method for sensing flatness of a running sheet in which some conditions; such as nozzle urging force, gas pressures, tension for the sheet etc.; are limited within rather narrow ranges for facilitating easier and more accurate sensing.

A further object of the present invention is to provide an apparatus suitable for such objects as mentioned I above.

A further object of the present invention is to provide an apparatus in which the inner-diameter of the nozzles is selected from a narrow range or the ratio of the outer to the inner diameter is determined in a narrow range.

In furtherance of these and other objects, a principle feature of the present invention in a method of and apparatus for more easily controlling the nozzle urging force and the thickness of the gas layer between the nozzle and the sheet. Another feature is the more accurate sensing of flatness or shape of the sheet by eliminating interaction between the two gas pressures p and q through the independent control of the two pressures. Further features include easier determination of a suitable nozzle urging force for a given sheet thickness; easier determination of the proper span or tension in relation to the sensibility of the sensor; and easier determination of suitable inner and outer diameters of the nozzle.

The method and apparatus of the instant invention are characterized by a plurality of nozzles for sensing the flatness or the shape of a metal sheet or strip running under a predetermined tension T which are arranged laterally beneath the running sheet or strip in a separated and suspended state by a force W which urges each nozzle towards the sheet or strip. The urging force W is controlled by a force not exceeding 3 Kg and by a gas pressure q which is to be controlled independently from the jetting pressure p of the gas flowing from the nozzles.

The under-sheet arrangement is convenient in maintenance and operation supervising of the strip mill and and can prevent nozzles from touching the sheet end which is often upwardly flared. Also, the under-sheet arrangement ensures that the nozzle is positioned lowest When not operated and does not stain the sheet surface with drain or oil droppings from the nozzle units.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a cross sectional view of one embodiment of the nozzle of the present invention appropriately position below a tensioned sheet.

FIGS. 2 and 3 are graphs showing characteristic curves of deflection variation against tension in which nozzle urging force is taken as a parameter for different lengths of span.

FIGS. 4-7 are graphs showing characteristic curves of jetting gas layer thickness against nozzle urging force in which jetting gas pressure is taken as a parameter.

FIG. 8 is a vertical cross-sectional view of another embodiment of the nozzle of the present invention.

FIGS. 9-ll are vertical cross-sectional views of a variety of other embodiments of the nozzle of the present invention.

DETAILED DESCRIPTION Referring to FIG. 1, a running metal sheet or strip S which may be aluminum is rolled between workrollers r, and r and pressed by back-up rollers R and R respectively.

These rollers are rotatably supported by a base structure (not shown). The free or unsupported span be tween rollers r r and the deflector roller r 3 is supported by a fixed tension in the longitudinal direction.

Under the strip S there are arranged laterally a plurality of spaced apart sensing nozzle units N (in FIG. 1 a single unit is illustrated for simplicity). The central axis of the nozzle unit N is arranged normal to the direction of the running sheet S, in a non-contacting and suspended state. A thin layer of flowing gas which is supplied to a nozzle head 2 of a nozzle body 1 through a hose connection 7 which is connected to a reservoir (not shown) of a controllable pressure p. The nozzle body 1 is continuously urged in longitudinal direction by flowing gas which is introduced into a cylinder 1 through a hose connection 8 which is connected to a reservoir (not shown) of independently controllable pressure q. The cylinder 1' is fixedly supported by a suitable structure (not shown). The pressures p and q are to be controlled independently, i.e., without mutual interference.

Under a normal condition a certain constant deflection 8 of the sheet S is observed since the position of a nozzle does not change. However, the deflection increases when buckling of the Sheet S occurs due to the upward longitudinal movement of the nozzle. Variation of the deflection may be sensed by an electric differential transformer (see numeral 13 in FIG.

The deflection variation A 8 is equivalent to the sensibility of the sensing unit. Referring now to FIGS. 2 and 3, there is shown the relationship between the deflection variation A 6 and tension T of the sheet, wherein the nozzle urging force W is taken as a parameter and different groups of curves A, B, and C are shown for different spans or thicknesses.

Referring again to FIGS. 2 and 3, it is clearly understood that all the curves show a common tendency of the deflection variation A 6 to decrease rapidly at first but slowly as tension T increases and to eventually approach a constant value. In FIGS. 2 and 3 the solid lines show the deflection variation A 8 at the center position of a sheet, while the broken lines show the deflection variation A 67 at the quarter position or a quarter of the distance from the sheet edge.

The curves shown as A in FIG. 2 are taken for a stationary sheet of aluminum having a width of 1,000 mm, a thickness of 0.76 mm and a span of 1,000 mm. The curves shown as B in FIG. 2 are taken for a stationary sheet of aluminum having a width of 795 mm, a thickness of 1.2 mm and a span of 1,670 mm. The curves shown as A in FIG. 3 are taken for a stationary sheet of aluminum having a width of 1,000 mm. a thickness of 0.76 mm and a span of 2,000 mm.

From these curves'it should be understood that the deflection variation or the sensibility of the sensor decreaes rapidly at first as the tension T increases, but has a tendency to approacha constant value for larger values of T and also increases as the span increases.

The tension of the sheet to be processed is usually determined in a certain suitable range according to the processing method to be taken, for example, 3-8 Kg/mm for rolling or 2-5Kg/mm for tension rollerlevelling. Therefore, once material, processing method and length of free span, etc. are specified the optimum tension ranges may be selected, under which an optimum urging force for nozzles may be determined to have a suitable sensibility.

The nozzle urging force W apparently relates to the layer thickness 1 of the gas flowing from the nozzle.

Referring now to FIGS. 4-7, the layer thickness t of the gas flwong from the nozzle of the instant invention is approximately proportional to the gas pressure p (within a practical range of under 5 Kg/cm Further, the layer thickness t shows a tendency to decrease as the nozzle urging force W increases and a tendency to approach a constant value for large values of W. Such a tendency appears more conspicuous as the inner diameter of the nozzle increases. For nozzle inner diameters under a certain limit, the layer thicknes will be too thin to maintain the separation between the nozzle and the sheet. Accordingly, it becomes difficult to maintain a non-contacting condition between the nozzle and the sheet for nozzle inner diameters of 3 mm or less and gas pressures not exceeding 5 Kg/cm On the other hand larger nozzle inner diameters will increase energy loss, although it is advantageous to maintain a thick gas layer for a larger urging force W.

Thus it should be understood that the nozzle inner diameter is preferrably determined within a certain range, i.e., practically 3-8 in millimeters, and accordingly the nozzle urging force W can be determined as any value not exceeding 3 Kg.

In carrying out the present invention such conditions as: the nozzle urging force of not more than 3 Kg; the nozzle inner diameter ranging from 3 to 8 millimeters; and the pressure of the nozzle exhausting gas of not more than 5 Kg/cm are particularly important.

The nozzle outer diameter should be determined in relation to the nozzle inner diameter, and experiments show that an outer to inner diameter ratio ranging from 3 to 6 allows a suitable layer thickness t for a relatively small nozzle urging force W.

According to the present invention when tension T and/or span length are given for a certain sheet material it will be easy to determine, by adjusting gas pressure q, a certain range of upwardly urging force W for which a nozzle having suitably sized inner and outer diameters can be selected. Then all of the necessary controls can be obtained by adjusting the gas pressures p and q, both of which are remotely or independently controllable. Thus, desirable layer thickness t and/or sensibility can be obtained.

Referring now to FIGS. 8-11, several embodiments for the apparatus according to this invention are illustrated. In all of the figures S designates a metal sheet or strip running under tension. A nozzle 2 is an integral part of a nozzle system or body 1, through which an axial passage 9 is provided.

More particularly, FIGS. 8-11 show a pair of housings or cylinders 4 and 6 provided in a separated state. The housings which may bemounted on a fixed frame (not shown) slidably accomodate nozzle extension 3 or middle part5. The cylinder 4 in FIG. 8 and the bushing style housing 4 in FIGS. 9-10 are supplied with pressurized air from a reservoir (not shown) through a hose 7a (see FIG. 8) which is connected in a pressure tight manner to a connector 7. The pressurized air is supplied to the connector 7 under a pressure p controlled by a pressure-control valve 7b as shown in FIG. 8. The supplied air is introduced to the nozzle 2 through the passage 9, directly from the cylinder 4 in FIG. 8 or via one or more openings 11 bored in a recessed portion 10 in the cases of FIGS. 9-10. The supplied air is exhausted from a nozzle opening 2a in the nozzle 2 to form a layer of jetting gas between the sheet S and the top surface 2b of the nozzle 2.

Compressed air (or any pressured fluid) is supplied from a supply source (not shown) through a hose 8a connected in a pressure-tight manner to a connector 8, under a pressure q controlled by a pressure-control valve 8b as shown in FIG. 8. The controllable fluid pressure q is applied to the bottom surface 3a of a nozzle extension 3 in FIG. 9-10. and to an enlarged part 5a of the middle part 5 of the nozzle body 1 in FIG. 11, to uge the nozzle body 1 upward. The sliding surfaces of the enlarged part 5 and the nozzle extension 3 are provided with small grooves 5b, 3b respectively.

Thus, the nozzle 2 is suspendedly supported in the vertical direction due to a balance between the jet reaction and the force urging the nozzle 2 upward. However, the jet reaction force is also balanced with a reaction of the deflected portion of the sheet, that is, the nozzle urging force W is balanced with the reaction of the deflected portion of the sheet.

The jet flow from the nozzle will not deliver any force to the sheet, but simply produces a thin bearing layer of flowing gas. Therefore, the force to yield a deflection on the sheet (f is produced only from the force to urge the nozzle (f that is, the former force (f is exactly equal to the latter (f However, the pressure of gas p to form a jet flow gives an almost proportional effect to the thickness of a bearing gas layer as shown in FIGS. 4-7.

Therefore, a plurality of spaced apart nozzles arranged laterally under the running sheet maintain a constant level or position under a constant pressure p; but once a buckling condition appears on the sheet, the position of the nozzle confronting the buckling portion will vary its vertical position and cause the up-anddown logitudinal movement ofthe nozzle. The amount of deflection may be transformed into an electrical signal by a defferential transformer 13 (see FIG. or a magnetic scale (see FIG. 9).

It is to be understood that the movable nozzle can be used only to produce a deflection on the sheet and the variation in the amount of deflection can be measured from the opposite side of the sheet without contact by measuring the variation of electric static capacity between the sheet and a flat metal part positioned on the opposite side of the sheet (not shown) or by measuring the eddy current induced on a metal part (not shown) positioned on the opposite side of the sheet.

The difference in the amount of deflection between a plurality of nozzles laterally arranged permits determination of the shape or flatness of the sheet. When such sensing units are arranged at the outlet of a cold rolling mill or a tension roller leveller, an automatic control of the flatness of products can be achieved by comparing the signal from the sensing units with a command signal and giving a defferential input to a flatness control device, such as a crown-control device or a roller-diameter control device.

It will be obvious to those skilled in the art that various changes may be made without departing from the scope of the invention and the invention is not to be considered limited to what is shown in the drawings and described in the specification.

We claim:

1. A method of sensing flatness of a sheet freely running between successive rollers under a predetermined tension, by comparing up-and-down longitudinal displacement between a plural number of gas-jetting nozzles arranged in a lateral direction of the sheet, spacedly apart and each of the nozzles is slidably supported by at least a cylinder spacedly fixed in a suspended applying a controllable force to urge said nozzle upwardly by applying to said nozzle another pressure of gas which is independently controllable from said gas jetting pressure.

2. The method of claim 1 wherein said controllable force to urge nozzle upwardly does not exceed 3 kg for any nozzle.

3. The method of claim 2 wherein both said pressure for jetting and said pressure for urging said nozzle upwardly do not exceed 5 Kg/cm 4. The method of claim 3 wherein said predetermined tension of said freely running sheet supported between successive rolls of a cold rolling mill or tension roller leveller is determined to an optimum value within a range of 2-5 Kg/mm and said nozzle urging force is selected as an optimum value not exceeding 3 Kg, in consideration of the sensibility of said sensing units for a given material, thickness and the free span.

5. An apparatus for sensing flatness of a sheet running freely between successive rollers under a predetermined tension by comparing the axial displacement between a plurality of spaced apart nozzles arranged laterally, each nozzle being in a suspended state due to a balance between a jet of gas flowing out from said nozzle and a force urging said nozzle upward comprising:

cylinder means for slidably holding said nozzle in a suspended state;

gas supplying means connected to said nozzle for forming said jet of gas flowing out from said nozzle and force urging said nozzle upward, said jet having ajetting gas pressure and said force having a nozzle urging gas pressure,

first valve means connected to said gas supplying means for controlling the jetting gas pressure of said compressed gas;

second valve means connected to said gas supplying means for controlling said nozzle urging gas pressure independently from said jetting gas pressure.

6. The apparatus of claim 5 wherein said nozzle inner-diameter is between 3 to 8 millimeters.

7. The apparatus of claim 6 wherein the ratio of the outer-diameter to the inner-diameter is between 3 to 6.

8. The apparatus of claim 5 wherein said nozzle includes a piston integral with said nozzle.

9. The apparatus of claim 5 wherein said nozzle includes a cut-away recessed portion and means for allowing said compressed gas to flow into said recessed portion. 

1. A method of sensing flatness of a sheet freely running between successive rollers under a predetermined tension, by comparing up-and-down longitudinal displacement between a plural number of gas-jetting nozzles arranged in a lateral direction of the sheet, spacedly apart and each of the nozzles is slidably supported by at least a cylinder spacedly fixed in a suspended state in the longitudinal direction due to a balance between the jet reaction and a force to urge said nozzle upward comprises the steps of: arranging a plural number of sensing units including said nozzles underneath said sheet at a right angle thereto; feeding compressed gas at a controllably predetermined pressure through each of said nozzles to form a thin layer of gas around the nozzle opening, applying a controllable force to urge said nozzle upwardly by applying to said nozzle another pressure of gas which is independently controllable from said gas jetting pressure.
 2. The method of claim 1 wherein said controllable force to urge nozzle upwardly does not exceed 3 Kg for any nozzle.
 3. The method of claim 2 wherein both said pressure for jetting and said pressure for urging said nozzle upwardly do not exceed 5 Kg/cm2.
 4. The method of claim 3 wherein said predetermined tension of said freely running sheet supported between successive rolls of a cold rolling mill or tension roller leveller is determined to an optimum value within a range of 2-5 Kg/mm2 and said nozzle urging force is selected as an optimum value not exceeding 3 Kg, in consideration of the sensibility of said sensing units for a given material, thickness and the free span.
 5. An apparatus for sensing flatness of a sheet running freely between successive rollers under a predetermined tension by comparing the axial displacement between a plurality of spaced apart nozzles arranged laterally, each nozzle being in a suspended state due to a balance between a jet of gas flowing out from said nozzle and a force urging said nozzle upward comprising: cylinder means for slidably holding said nozzle in a suspended state; gas supplying means connected to said nozzle for forming said jet of gas flowing out from said nozzle and force urging said nozzle upward, said jet having a jetting gas pressure and said force having a nozzle urging gas pressure, first valve means connected to said gas supplying means for controlling the jetting gas pressure of said compressed gas; second valve means connected to said gas supplying means for controlling said nozzle urging gas pressure independently from said jetting gas pressure.
 6. The apparatus of claim 5 wherein said nozzle inner-diameter is between 3 to 8 millimeters.
 7. The apparatus of claim 6 wherein the ratio of the outer-diameter to the inner-diameter is between 3 to
 6. 8. The apparatus of claim 5 wherein said nozzle includes a piston integral with said nozzle.
 9. The apparatus of claim 5 wherein said nozzle includes a cut-away recessed portion and means for allowing said compressed gas to flow into said recessed portion. 